Onix OA 601 Humming ?

HI, I have two Onix OA601's, one I have had about a year and one that I have purchaced recently, I was very exited about getting home so that I could try it out, only to find that hums as soon as you conncet the phono input cables, additionally when you turn it offf the LED goes out immedately, and does not dim slowly like all the other Onix amps I have owned. Does any one have any ideas?? Pls....:confused: :confused: :confused: